We propose to examine whether the onset of diabetes mellitus induces alterations in the structural and functional properties of platelet surface membranes. Intact platelets or purified platelet plasma membranes obtained from diabetic patients and controls will be labeled with fatty acid, phospholipid or sphingolipid spin probes, I(m,n), and the respective fluidities will be compared. Previous studies indicate that the electron spin resonance spectra of I(m,n)-labeled whole platelets or isolated plasma membranes provide information on the surface membrane environment of the probe. In parallel functional studies, aggregating agents will be tested for their in vitro effects on the release reaction and the aggregation of diabetic and control platelets. The release reaction will be assessed by measuring the secretion of 14C-serotonin, while aggregation will be determined employing aggregometry techniques. Such studies may define whether alterations in membrane fluidity are related to the known accelerated platelet function in the diabetic. We will also examine whether structural/functional aberrations in platelets resulting specifically from chronic hyperglycemia and insulin deficiency are correlated with the degree of control of the disease, and the serum levels of erythrocyte glycohemoglobin. The possibility that an agent present in diabetic plasma perturbs the fluidity of platelet surface membranes or platelet functions will also be investigated. Lastly, studies will be conducted to determine if the lipid fluidity is involved in the stimulation of platelets by aggregating agents, and also whether the state of membrane lipids modulates platelet function. Agents which perturb the membrane fluidity, such as temperature alterations, neutral and charged local anesthetics, cholesterol and the cholesterol-complexing drugs filipin and digitonin, and the cations Ca2 ion, Mg2 ion, and La3 ion will be tested for their respective effects on fluidity, aggregation and the release reaction. Furthermore, aggregating and release-inducing agents will be examined for direct effects on the fluidity of I(m,n)-labeled platelet membranes.